Printers for printing desired information such as text and images on a sheet-like printing medium such as paper or film are available as the information output devices of word processors, personal computers and facsimile machines, by way of example.
Various techniques are known for application to printing methods employed by printers. Ink-jet technology has become the focus of attention in recent years because of its ability to print on a printing medium such as paper without contacting the medium, the facility with which it lends itself to color printing and the quietness with which printing is performed. A serial printing method is employed most widely as the ink-jet printing method because of the advantages of lower cost and smaller size. The serial printing method employs a mounted printhead for jetting ink in accordance with desired print information. Printing is carried out while the printhead is scanned back and forth in a direction that intersects the direction in which the printing medium such as paper is fed.
The typical serial-type printer has a buffer memory for storing print data. Print data that has been stored in the buffer memory is transferred to the printhead and the printhead is made to scan in a main-scan direction to print on the printing paper.
The minimum unit of print data stored in the buffer memory is, e.g., 8 bits or 16 bits, and the data is handled unit by unit. The minimum unit (transport pitch) of transport distance of the printing medium is set to a distance for printing data in an amount that is a whole-number multiple of the minimum unit of print data.
With the conventional printer described above, the transport pitch of the printing medium is set together with the number of printing elements used in a single scan in each printing mode at the design stage of the printer. The transport pitch cannot be changed later. This means that the printing elements used in the printing of each raster is set permanently.
As a consequence, it is required that the mechanical parts and motors employed in the transport mechanism used in printers of the same model be of high precision with little variation from one to another. This raises the overall cost of the apparatus.
Further, it is not possible to change and update printing-mode specifications, e.g., to increase the number of scans made in multiple-pass printing. Furthermore, in a color printer having printheads with different numbers of printing elements, it is difficult to achieve agreement among the lengths of the printing areas (widths of the bands) of all colors in the direction of transport.